Group “Fundamental Interactions”

The current understanding of the dynamics of the physical world is in terms of three fundamental interactions: the gravitational, electroweak and strong forces. These are expected to account for the full complexity of the world, ranging from subnuclear ($10^-20$ m) to cosmological ($10^26$ m) scales. In spite of this huge range in scales, all forces are described in a coherent manner by similar theories based on the two major revolutions in physics of the twentieth century, quantum physics and relativity. These theories are constructed using field theory, geometry and group theory.

The mathematical investigation of these three theories and possible extensions are pursued in the group by the team Geometry, Physics and Symmetries.

The Particle team is specialized in the confrontation of models with observational data on subnuclear scale, using in particular large-scale numerical simulations in lattice QCD, effective field theories, low-energy precision experiments and dark matter searches.

During the last twenty-five years cosmology has witnessed a breathtaking acquisition of new observational data that appear to challenge the theory. The Cosmology team concentrates on the two major enigmas, the accelerated expansion of the universe and the anomalies in the dynamics and the clustering of matter at cosmological scales.

The coherence of the overall picture is broken in one point: In spite of intense efforts, we still lack a quantum description of gravity. The Quantum Gravity team has taken up this challenge and in spite of being the youngest of the four teams, it is already one of the leading teams world-wide. Two of its current themes are the investigation of what happens at the center of black holes and the physics of the big bang.

In connection with particle physics experiments and dark matter searches, we test the limits of the Standard Model and explore models of new fundamental physics that could explain some of its shortcomings.

Our activities are centered on the mathematical description of physical laws, in particular fundamental interactions. They lead to the emergence of new mathematical structures needing a dedicated study or to direct physical applications.

We study the large-scale structure of spacetime. Our activities concern the interpretation of enigmatic phenomena such as the acceleration of the expansion of the universe (dark energy problem) or the anomalies in the dynamics and clustering of matter in the universe (dark matter problem).

Our team studies the quantum properties of gravity. Equivalently: the quantum aspects of time and space. It is leader in the Loop Quantum Gravity approach. This is applied to cosmology and black hole physics, searching for experimental signatures.